Where small volumes of paint or other finishes have required re-mixing, it is well known for a user to achieve this by manually stirring the mixture with a stick or spatula. Where such mixing or stirring is more arduous, it has long been suggested that such manual stirring and mixing may be more efficiently achieved by a device utilising an electric motor, see for example
PTL 0001: GB 11010/35 (GEORG CAULTER). 1935 Apr. 9.
Published Document
PTL 0002: U.S. Pat. No. 2,799,485 (ISAAC SILVERMAN). 1957 Jul. 16.
describes an attachment that can be fitted in the chuck of an ordinary electric hand drill to mix or stir the contents of a paint can or other container. The attachment is formed from an elongated shaft having a mixing blade attached to its lower end and an extension stem, which projects below the mixing blade to space the blade away from the bottom of the container. The problem with this type of device is that although rotation of the elongated shaft and mixing blade is driven by an electric drill, the sweep of the mixing blade is significantly less than the diameter of the container and therefore the user still has to move the attachment around in the container contents manually to ensure everything is mixed adequately. This requires some degree of effort and skill to hold and manoeuvre the drill and mixing attachment, while stirring to mix components which have become stratified, with heavy components typically sinking to the bottom of the container in a thick sludge like manner.
To overcome this problem,
PTL 0003: U.S. Pat. No. 4,083,653 (HUGH A. STIFFLER). 1978 Apr. 11.
suggests a stirring device that employs a shaft-mounted hub with five axially nested, radially extendable fins shaped to provide both compact nesting of the five fins and also to provide ample surface area when extended for stirring. However, this device is complex, as is the mode of operation described in the document and it is difficult to clean effectively. Although holes are shown distributed along the fins in FIGS. 3 and 4, this document specifically teaches away from the formation of a vortex during stirring (see column 3, lines 16 to 17).
In another example,
PTL 0004: U.S. Pat. No. 4,422,770 (GEIBLE HARRY F). 1983 Dec. 27.
describes a paint stirrer, which is attached to a second lid assembly. The second lid assembly comprises a lid to prevent splashes during use and a stirring rod which projects through the lid and may be driven by an electric drill. The stirring rod has a bottom portion which is sized and shaped to lie close to the peripheral and the bottom walls of the container before terminating at the centre of the internal volume thereof, to ensure complete stirring of the paint within the container, without any requirement for the user to manually manoeuvre the drill around in the paint to ensure complete mixing.
PTL 0005: U.S. Pat. No. 5,090,816 (THOMAS SOCHA). 1992 Feb. 25.
describes yet another mixing device having a rotatable impeller with multiple blades. Each blade of the impeller has an optimal angle of attack with respect to the fluid being mixed and each blade has an aperture (or elliptical hole) for an improved flow stream of fluid through the aperture upon mixing. Again, this device is difficult to clean and package as the impeller blades extend radially outwardly from the rotatable shaft. The blades are arranged at a particular angle of attack with respect to the fluid and the shaft axis.
Finally,
PTL 0006: US 2009/0141586 A (DYER, III). 2009 Jun. 4.
describes yet another mixing rod having attached blades of the propeller or impeller type that are elongated flat-plate, curved or contoured, and have arched projections so that the material to be blended or mixed can flow through (i.e. under the arch) when the blades are rotated. Optionally, the blades also have apertures or holes, which when present are located under or otherwise adjacent to the arched projections. As described above, this device is difficult to clean and package as the impeller blades extend radially outward from the shaft.